enable to handle multibyte filenames

I got tons of "Write failed: Wide character in syswrite at \
/usr/lib/perl/5.12/IO/Handle.pm line 207." errors when I tried to handle
multi-byte filenames through 'render_file' method.

Filenames encoded in UTF-8 can suppress these errors.

I added a little code fix which encodes/decodes filenames
and test scripts which contains multibyte characters.